Serious infections require early treatment with effective antibiotics [Mandell et al. (1995) Principles and practice of infectious diseases. 4th edition. Churchill Livingstone, New York]. Because definitive identification of most bacteria, using a combination of culture, morphological and biochemical tests, usually requires several days to complete, most infectious diseases are treated empirically with broad spectrum antibiotics [Weinstein (1968) Pediatr. Clin. North Am. 15:141-156; Moellering (1974) In: Seminar on Gram-Negative Infections. St. Louis 1974:5; Cassiere et al. (1998) Dis. Mon. 44:613-675]. The emergence of multidrug-resistant bacteria has reduced the effectiveness of this practice. It has become increasingly difficult to find antibiotics (or combinations of antibiotics) that are reliably effective against all of the etiologic organisms of a specific syndrome. This problem is exacerbated where an unusual microbial (e.g., bacterial. mycoplasmal, viral, or parasitic) agent results in an infectious syndrome that can be confused with one caused by one (or more) more common pathogens. Simpler and more rapid identification methods and subsequent pathogen-specific therapy are becoming increasingly important in the treatment of infectious diseases [Casadevall (1996) Clin Infect Dis. 23:790-794]. U.S. Pat. Nos. 5,487,972; 5,538,848; 5,925,517, published International Application No. WO 97/39008, and International Application No. PCT/US99/17145 are incorporated herein by reference in their entirety.